Process for producing acrylic acid



Feb. 27, 1962 w. REPPE ETAL 3,023,237

PROCESS FOR PRODUCING ACRYLIC ACID Filed May 1, 1959 Q X X I ip A F H XG SEPARATOR X LII. 1 A M95 It A D C B X I X INVENTORS: WALTER REPPE BYROBERT STADLER ATT'YS A 1 3,333,233 Patented Feb. 27, 1962 3,023.237PROCESS FOR PRODUCING ACRYLEC ACID Walter Reppe and Robert Stadler,Heidelberg, Germany,

assignors to Badische Anilin- 83 Soda-Fabrik Akttengescllschaft,Ludwigshafen (Rhine), Germany Filed May 1, 1959., Ser. No. 818,279Claims priority, application Germany Feb. 17, 1953 18 Claims.v (Cl.260-533) This invention relates to the production of acrylic acid by thecarbonylation of acetylene in the presence of water, and moreparticularly, to an improved method of producing' acrylic acid in anovel aqueous reaction medium containing an activated carbonylationcatalyst.

It has already been proposed to produce acrylic acid by bringingacetylene and carbon monoxide into contact with water in the presence ofcatalytic quantities of compounds of metals of the Iron Group, i.e.iron, nickel or cobalt, the reaction being carried out undersuper-atmospheric pressures and at elevated temperatures. The same typeof catalytic reaction has also been employed in the production ofacrylic acid esters by substituting alcohols in place of water. Theimproved production of such acrylic acid esters forms the subject matterof our copending application, Serial No. 468,580, filed November 12,1954 and issued as US. Patent 2,883,418. The present application is acontinuation-in-part of our prior copending application, Serial No.410,179, filed February 15, 1954, abandoned after the filing of thisapplication.

The catalytic methods of producing acrylic acid and acrylic acid estersare generally conceded to be superior to the vairous knownstoichiometric methods in which nickel carbonyl in substantial amountsis required as an essential ingredient of the reaction mixture. Sincenickel carbonyl is an expensive and poisonous compound, much time andeffort has been devoted in research to find a commercially usefulcatalytic method whereby the use of nickel carbonyl can be avoided.Various modifications of the catalytic method have therefore beensuggested, and while fairly satisfactory results have been obtained inthe synthesis of acrylic acid esters, the results when producing acrylicacid itself have been especially disappointing and unsatisfactory on anindustrial scale. It has been our observation that the acetyleneemployed as a starting material tends to be transformed intoacetaldehyde during the synthesis of acrylic acid. The activity of theknown catalysts under known reaction conditions thereby decreasesrelatively quickly so as to substantially reduce the rate of conversionwith correspondingly low yields.

The prior art, including that appearing in our copending parentapplication, which is pertinent to the manufacture of acrylic acid maybe set forth as follows:

In the manufacture of acrylic compounds such as acrylic acid oracrylicacid esters by the so-called stoichi-' ometric method (GermanPatents 855,110, 872,042, 872,341 and 872,939), stoichiometric amountsof a metal carbonyl are reacted with acetylene an a compound with areactive hydrogen atom such as Water or an alcohol in the presence of anacid. This process can be illustrated by the following equation: I

It is a disadvantage of this process that the entire carbon monoxiderequired for the carbonylation of the acetylene must be furnished by theexpensive and poisonous metal carbonyls.

In the production of acrylic acid and its esters by the so-calledcatalytic method (German Patents 854,948, 881,650 and 805,641, copendingapplication Serial No. 288,534, now Patent 2,738,364, and J. W. Reppe,Acetylene Chemistry, C. A. Meyer & Co., Inc., New York (1949), page161), acetylene, free carbon monoxide and a compound with a reactivehydrogen atom are reacted in the presence of catalytic amounts ofcarbonyl-forming metals or the oxides or salts of such metals. For theformation of acrylic acid this process can be illus trated by theequation catalyst CzHz-l-CO-l-HnO CHFCHOOOH While nickel carbonyl is themost suitable catalyst .in such a process it has the disadvantage offavoring the formation of by-products such as acetaldehyde andvinylbromide.

Various additives such as metals, metal compounds or complex-formingorganic compounds of phosphorus, arsenic, antimony and nitrogen havebeen suggested in order to increase the activity and the life of thecatalyst employed in the catalytic synthesis of acrylic compounds fromacetylene, carbon monoxide and compounds containing a reactive hydrogenatom.

These processes yield fairly satisfactory results when employed for thesynthesis of acrylic acid esters. However, in the production of freeacrylic acid, such processes work only with low yields and poorthroughputs. Furthermore, the carbonyl-forming metal catalysts such asnickel halides have been employed according to the prior art inrelatively high amounts and the catalyst forms thereby with the liquidreaction medium a non-homogeneous system.

U.S. Patent 2,613,222 shows the preparation of acrylic acid and itsanhydrides by a process in which the catalytic reaction between water,acetylene and carbonyl monoxide must be first initiated by astoichiometric interaction between water, acetylene, nickel carbonyl andan acid. The stoichiometric reaction which precedes the catalyticreaction must furthermore be maintained while there is imposed upon itthe catalytic reaction. In such a process at least 35%, but preferably40% to 50% of the total carbon monoxide is carbon monoxide supplied bynickel carbonyl.

It is a disadvantage of this process that a greatdeal of the reactionmust be performed by the stoichiometric method which entails a highdemand of pre-formed nickel carbonyl, therefore requiring particularsafety measures.

One object of the invention is to avoid the formation of by-products,especially acetaldehyde, in the production of acrylic acid by employinga particular activated catalyst.

Another object of the invention is to provide animproved production ofacrylic acid in which the catalyst has a long life and its activity isincreased and maintained.

Yet another object of the invention is to produce acrylic acid with aspecific catalyst and under reaction conditions,

including the use of a novel aqueous reaction medium,

of acrylic acid on a large scale. These and other objects and advantagesof the invention will become more apparent upon a consideration of thefollowing detailed specification.

We have found in accordance with the present invention that in carryingout the carbonylation of acetylene in the presence of water it is veryadvantageous to use an excess by volume of an organic solvent withreference to the volume of Water employed, said organic solvent beinginert to acetylene under the reaction conditions and miscible withwater. We have further found that the amount of the carbonylationcatalyst, i.e. of a compound derived from a metal of the Iron Group,should be so chosen that this catalyst is homogeneously dissolved in theliquid reaction medium constituted by the mixture of water and inertorganic solvent. It has also been established by us that the catalystsshould be activated by including in the reaction medium a small amountof a soluble copper compound.

As organic solvents we prefer oxygen-containing watermiscible liquidswhich are inert under the reaction conditions, i.e. which are notirreversibly changed by the presence of water and which are not able toreact with acetylene or carbon monoxide. The solvents, therefore, shouldnot contain free hydroxy, mercapto or carboxy groups, olefinic oracetylenic linkages, or primary or secondary amino groups. Their boilingpoint should preferably be below that of acrylic acid, i.e. below about142 C. Preferred solvents for our process are cyclic ethers, such astetrahydrofurane, -pyrane and 1,4-dioxane, and also fully saturatedaliphatic ketones, such as acetone, methyl ethyl and diethyl ketone.Another group of useful solvents consists of cyclic esters and amides,such as butyrolactone or N-lower alkyl-lactams, in particular N-alkyl-pyrrolidones, such as the methyl and ethyl compounds.Tetrahydrofurane, whenever available, is a very satisfactory solvent,since it has a relatively low boiling point and a high dissolving powerfor acetylene, and is otherwise absolutely inert. It may be easily andcheaply recovered and used again.

While in our process it is possible to work with a slight excess of thesolvent, e.g. 60 parts by volume for 40 parts by volume of water, weprefer to employ much higher excesses of the organic solvent in theworking liquid. We suggest to have from 75 to 95 percent by volume ofthe solvent and from 25 to percent of water. With some solvents,especially tetrahydrofurane, it is quite satisfactory to work with fromto percent by volume of water. It is also possible to work with mixturesof two or more organic solvents.

The .catalysts used in performing our invention are compounds of metalsof the iron group. While both iron and cobalt show carbonylationactivity. which makes them potential technical catalysts, we prefer towork with nickel compounds. Since the catalysts should in any casecontain halogen either in a free or in a chemically combined. form, thesimplest way is to use the halides, especially nickel chloride andbromide and. iodides. The iodides are very active, but some care must beexercised to avoid corrosion. We may also use metal carbonyls preparedper se, provided there is present halogen, e.g. free bromine, hydrogenbromide, halides of other metals andthe like. Thus, mixtures of nickel,cobalt or iron carbonyls in combination with other metal halides areworkable catalysts. At the same time, it is a special advantage of theinvention that such metal carbonyls can be avoided, their inclusionherein merely illustrating the use of soluble nickel compounds. We mayalso build up our catalyst from several metals of the Iron Group.

As activators we use copper compounds which are soluble in the reactionmedium. Since the reaction has to be carried out in the presence ofhalogen, it is preferred to use the copper as a halide, e.g. chloride,bromide or iodide. Copper sulfate, acetate, propionate and otherwater-soluble salts may be used together with halide ions.

Sometimes it has been found useful to add a small amount (less than 1percent by weight) of powdered copper. However, the process worksgenerally quite satisfactorily without it. Furthermore, a small amountof halogen hydride, e.g. 0.1 to 1 percent by weight of hydrogen bromide,is useful.

The amount of the catalyst required is relatively small and depends tosome extent on the kind of metal, which compound thereof is used, and onthe composition of the liquid reaction medium. Generally speaking, theconcentration is a catalytic quantity, i .e. not more than 2 percent andpreferably not more than 0.5 percent by weight of the compound of themetal of the Iron Group, calculated on the liquid reaction medium.Satisfactory results have been obtained in the range of about 0.05 to 2percent. The amount of the copper compound used as an activator is ingeneral somewhat lower than that of the catalyst, i.e. usually not morethan 0.1 percent by weight of the copper compound calculated on theliquid reaction medium. Satisfactory results have been obtained fromabout 0.02 percent by weight of the activator up to as much as an equalamount with reference to. a nickel halide employed in the reactionmedium.

The reaction conditions used in the carbonylation are within theconventional range. We prefer to use acetylene and carbon monoxide insubstantially equimolecular ratios, but the C H :CO ratio may varywithin wide limits, e.g. between 0.5 :1 to 1205. When working with acirculating gas, a 1:1 ratio is of advantage to avoid an accumulation ofthe excess component in the circulating gas. I

The working temperature is in the range of C. to 250 C., in particularbetween C. and 220 C. The carbonylation requires the use of increasedpressure. While in principle we may Work at pressures exceeding 5atmospheres, We found it more economic to ensure a high conversion rateby applying at least 20 atmospheres, e.g. up to 60 atmospheres, and anindividual partial pressure for acetylene and carbon monoxide of atleast 10 atmospheres. Pressure above 60 atmospheres, e.g. 70 to 90atmospheres, may also be used. However, the precautions necessary whenworking with acetylene at very high pressures are generally so expensivethat the gain in higher conversion tends to be cancelled.

The reaction may be carried out batchwise or continuously. In acontinuous process we may either work according to the trickling methodby leading the working liquid downwards through a reactor charged withfiller bodies while leading the gas mixture in the same or oppositedirection. We may as well introduce liquid and gases at the bottom of areactor and withdraw the mixture at the top thereof. The recovery ofacrylic acid from the reaction liquid is carried out eitherby extractionor'by fractional distillation. In this stage as well as duringthecarbonylation stage proper we may add the conventional polymerizationinhibitors.

The following examples will further illustrate how this invention may becarried out in practice.

Example 1 A stirring autoclave made from stainless steel is charged with2,500 cubic centimeters of tetrahydrofurane, 270 cubic centimeters ofwater, 6 grams of anhydrous nickel bromide, 1.5 grams of copper chlorideand 0.3 gram of hydroquinone. After having replaced the air by nitrogen,a mixture of equal parts by volume of acetylene and CO under 25atmospheres is pressed in and the Whole heated to 180 C. in the courseof about 90 minutes, thereby increasing the pressure to 46 atmospheres.By drawing a sample, homogeneousness of the working liquid is confirmed.As the reaction starts, it is accompanied by an increase in temperatureand a decrease in the pressure. The temperature is maintained at from184 to 188 C. and the pressure at from 44 to 50 atmospheres byreplenishing the gas mixture. After 2 hours the reaction is finished.The reaction mixture is then released from pressure (the release gascontains a little CO and distilled. 544 grams of acrylic acid are thusobtained and 56 grams of higher boiling products.

When working under otherwise identical conditions with grams of nickelchloride and 2 grams of copper bromide, the reaction takes a littlelonger. The yield amountsto 538 grams of acrylic acid.

Example 2 A homogeneous mixture of 2,365 cubic centimeters oftetrahydrofurane, 265 cubic centimeters of water, 4.55 grams of nickelcarbonyl, 1.82 grams of copper bromide and 0.9 gram of hydrogen bromideare treated with acetylene and CO (1:1.1) at from 186 to 196 C. under 40to 50 atmospheres. In the course of one hour, 656 grams of acrylic acid(86.8 percent yield) are formed. The high'boiling residue contains thetotal of the nickel in the form of acrylate. A small amount ofacetaldehyde is to be found in the first distillation fraction.

When changing the ratio of C H :CO to 1:1 or 1.1:1,

the results are substantially identicaL- When working in theabsence ofhydrogen bromide, the amount of high boiling residue is somewhat larger.

Example 3 Example 4 A stirring autoclave is charged with the followingmixture: 2,360 cubic centimeters of tetrahydrofurane, 240 cubiccentimeters of water, 3.6 grams of iron carbonyl, 1.8 grams of copperbromide, 2 grams of bromine and 0.3 gram of hydroquinone. In the mannerdescribed in Example 1 the mixture is treated at 200 to 208 C. withacetylene and CO (1:1) for 2 hours. There are obtained 631 grams ofacrylic acid, 150 grams of higher boiling products and a very smallquantity of acetaldehyde.

When working with iron bromide under otherwise identical conditions, theaddition of bromine may be dispensed with.

Example 5 In a stirring autoclave a solution consisting of 2,360 cubiccentimeters of tetrahydrofurane, 240 cubic centi meters of water, 2.27grams of nickel carbonyl, 0.15 gram of iron carbonyl, 1.65 grams ofcopper bromide and 1 gram ofbromine is treated for 1 hour at 184 to 193C. with acetylene and CO 1:1) under 40 to 50 atmospheres. Acrylic acid(598 grams) is obtained in an' 88.5 percent yield together with 77 gramsof higher boiling products.

Example 6 Under the conditions of Example 4, a mixture of 60 cubiccentimeters of tetrahydrofurane, 7 cubic centimeters of water, 0.1 gramof cobalt bromide and 0.1 gram of copper bromide is treated for 2hoursat 200 C. under 50 atmospheres. 7.74 grams of acrylic acid and 2.6grams of higher boiling products are formed.

To obtain the same result with cobalt chloride instead of the bromide,the reaction time has to be increased to 3 hours.

' reached 20 percent.

Example 7 v A homogeneous solution of 0.2 gram of nickel chloride and0.2 gram of copper chloride in a mixture of cubic centimeters of acetoneand 14 cubic centimeters of water is treated in a shaking autoclave atC. for 1 hour with a mixture ofacetylene and CO (1:1) while maintaininga pressure of 50 atmospheres. By distillation of the reaction mixturethere are obtained 20.25 grams of acrylic acid and 2.1 grams of higherboiling products.

Practically the same results are obtained when employing the bromidesinstead of the chlorides.

Example 8 A homogeneous solution of 0.1 gram of nickel bromide and 0.5gram of copper chloride in 80 cubic centimeters of an aqueous 88 percentdioxane are heated to to 197 C. while pressing in a mixture of acetyleneand CO under a pressure of 40 to 51 atmospheres. After 2 hours thereaction is finished. The working solution then contains 20.9 percent byweight of acrylic acid which is isolated by distillation.

Example 9 This example demonstrates a continuous process. I

Referring to the drawing, the reactor A, preferably a pressure-tighttube made from stainless steel and provided with heating and coolingdevices (not shown), is charged with the working liquid (solvent, waterand catalyst) through tube B. Through tube C a mixture of acetylene andcarbon monoxide is pressed into the reaction zone A by means of pump D.The reactor is then brought to reaction temperature while maintainingthe gas pressure. After the reaction has started which will be evidentfrom consumption of gas and the evolution of heat, the feeding of gas iscontinued and circulation maintained through line C via pump E.

When the acrylic acid concentration in the liquid has reached a certainlevel, e.g. between 10 and 20 percent by weight, fresh working liquid isintroduced through B and a corresponding amount of acrylic acid solutionwithdrawn through F. It is brought into a separator G where the pressureis released. The gases set free are brought back through line H and pumpJ into the main circulation line C. The acrylic acid solution iswithdrawn through line K and introduced into a distillation apparatus(not shown).

A stainless steel tube of 10 centimeters internal diameter and 6 meterslength (reactor A) to which lines for feeding and withdrawing gas andliquid are attached is filled with 30 liters of a working liquidconsisting of tetrahydrofurane, containing 12 to 15 percent of water,0.16 percent of nickel bromide, 0.05 percent of copper bromide, 0.1percent of hydrogen bromide and 0.01 percent of hydroquinone. Thereactor is slowly heated and acetylene-carbon monoxide mixture (1:1)under 46 to 205 C. while always maintaining 46 atmospheres.

After about one hour the acrylic acid concentration has Now 28 litersper hour of fresh working liquid are introduced and about 30 to 31liters per hour of acrylic acid solution withdrawn. Fresh gas mixture isintroduced at the rate of 5 cubic meters (N.T.P.) per hour.

The acrylic acid solution is withdrawn, and the acid isolated bydistillation. The tetrahydrofurane obtained as the first fraction isused again, after adding the other ingredients of the working solution.

From the foregoing description and examples, it can readily bedetermined that our catalytic process for producing acrylic acid showsan extraordinaryimprovement over prior procenes. Throughput and yield ofacrylic acid is substantially increased. A special advantage of largescale.

the invention resides in the use of inexpensive and readily obtainablecatalysts and activators, the nickel and copper halides being'especiallypreferred to obtain optimum results. Of course, other nickel and coppercompounds which are soluble in the reaction medium can also be employedin catalytic amounts.

It will also be noted that our improvement in the production of acrylicacid essentially requires a substantial excess of an inert watermiscible organic solvent with relation to water in the aqueous reactionmedium and furthermore requires a catalyst in which nickel, halogen andcopper must be present and dissolved to produce a homogeneous reactionmixture with the organic solvent and water. Under these conditions andthe specified temperatures and at high pressures it has been possible toprovide a process which can be easily carried out on a We claim:

1. A process for the production of acrylic acid which consistsessentially of contacting a gaseous mixture of acetylene and carbonmonoxide under a pressure exceeding atmospheres and at temperaturesbetween 150 and 250 C. with an aqueous reaction mixture of watercontaining at most 40% by volume of water and at least 60% by volume ofan organic, water-miscible inert solvent with respect to the totalvolume of said Water and said solvent, said aqueous reaction mixturehaving homogeneously dissolved therein ions of a metal of the Irongroup, halide ions from the group consisting of chloride, bromide andiodide, and copper ions.

2. A process for the production of acrylic acid which consistsessentially of contacting a gaseous'mixture of acetylene and carbonmonoxide under a pressure exceeding 5 atmospheres and at temperaturesbetween 150 and 250 C. with an aqueous reaction mixture of watercontaining at most 40% by volume of water and at least 60% by volume ofan organic, water-miscible inert solvent with respect to the totalvolume of said water and said solvent, said aqueous reaction mixturehaving homogeneously dissolved therein nickel ions, halide ions from thegroup consisting of chloride, bromide and iodide, and copper ions.

3. A process for the production of acrylic acid which consistsessentially of contacting a gaseous mixture of' acetylene and carbonmonoxide under a pressure exceeding 5 atmospheres and at temperaturesbetween 150 and 250 C. with an aqueous reaction mixture of Watercontaining at most 40% by volume of water and at least 60% by volume ofan organic, water-miscible inert solvent, with respect to the totalvolume of said water and said solvent, said aqueous reaction mixturehaving homogeneously dissolved therein a carbonylation catalystconsisting essentially of a nickel halide from the group consisting ofnickel chloride, nickel bromide and nickel iodide and a copper halidefrom the group consisting of copper chloride, copper bromide and copperiodide.

4. A process as set forth in claim 3, wherein one of the halides is abromide and the other is a chloride.

5. A process forthe production of acrylic acid which 1 consistsessentially of contacting a gaseous mixture of acetylene and carbonmonoxide under a pressure of at least atmospheres and at a temperaturebetween 170 and 220 C. with an aqueous reaction mixture containingbetween 5 and percent by volume of water and between 95 and 75 percentby volume of an organic, water-miscible inert solvent, said aqueousreaction mixture having homogeneously dissolved therein not more than 2percent by weight of nickel in the form of a nickel halide from thegroup consisting of nickel chloride, nickel bromide and nickel iodideand at most an equal amount of the copper halide from the groupconsisting of copper chloride, copper bromide and copper iodide.

6. A process as set forth in claim 5, wherein one of the halides is abromide and the other is a chloride.

7. A process as set forth in claim 5, wherein bromides are used as thehalides,

8. A process as set forth in claim 5, wherein chlorides are used as thehalides.

9. A process for the production of acrylic acid which consistsessentially of contacting a gaseous mixture of acetylene and carbonmonoxide under a pressure of at least 20 atmospheres and at atemperature between 170 and 220 C. with an aqueous reaction mixturecontaining between 5' and 25 percent. by volume of water and between and75 percent by volume of tetrahydrofurane, said aqueous reaction mixturehaving homogeneously dissolved therein ions of a metal of the Irongroup, halide ions from the group consisting of chloride, bromide andiodide, and copper ions.

10. A process for the production of acrylic acid which consistsessentially of contacting a gaseous mixture of acetylene and carbonmonoxide under a pressure of at least 20 atmospheres and at atemperature between and 220 C. with an aqueous reaction mixturecontaining between 5 and 25 percent by volume of water and between 95and 75 percent by volume of tetrahydrofurane, said aqueous reactionmixture having homogeneously' dissolved therein cobalt ions, halide ionsfrom the group consisting of chloride, bromide and iodide, and copperions.

11. A process for the production of acrylic acid which consistsessentially of contacting a gaseous mixture of acetylene and carbonmonoxide under a pressure of at least 20 atmospheres and at atemperature between 170 and 220 C. with an aqueous reaction mixturecontaining between 5 and 25 percent by volume of water and between 95and 75 percent by volume of tetrahydrofurane, said aqueous reactionmixture having homogeneously dissolved therein iron ions, halide ionsfrom the group consisting of chloride, bromide and iodide, and copperions.

12. A process for the production of acrylic acid which consistsessentially of contacting agaseous mixture of acetylene and carbonmonoxide under a pressure of at least 20 atmospheres and at atemperature between 170 and 220 C. with an aqueous reaction mixturecontaining between 5 and 25 percent by volume of water and between 95and 75 percent by volume of tetrahydrofurane, said aqueous reactionmixture having homogeneously dissolved therein nickel ions, halide ionsfrom the group consisting of chloride, bromide and iodide, and copperions.

13. A process for the production of acrylic acid which consistsessentially rt contacting a gaseous mixture of acetylene and carbonmonoxide under a pressure of at least 20 atmospheres and at atemperature between 170 and 220 C. with an aqueous reaction mixturecontaining between 5 and 25 percent by volume of water and between 95and 75 percent by volume of tetrahydrofurane, said aqueous reactionmixture having homogeneously dissolved therein a carbonylation catalystconsisting essentially of a nickel halide from the group consisting ofnickel chloride, nickel bromide and nickel iodide and a copper halidefrom the group consisting ofcopper chloride, copper bromide and copperiodide.

14. A process as set forth in claim 13, wherein one of the halides is abromide and the other is a chloride.

15. A process as set forth in claim 13, wherein bromides are used as thehalides.-

16. A process as set forth in claim 13, wherein chlorides are used asthe halides.

17. A process for the production of acrylic acid which consistsessentially of leading continuously through a vertically orientatedreaction zone under a pressure of at least 20 atmospheres and attemperatures between 170 and 220 C. a gaseous mixture of acetylene andcarbon monoxide and a liquid constituting an aqueous reaction mixture offrom 10 to 20 percent by volume of water and from 90 to '80 percent byvolume of tetrahydrofurane, said aqueous reaction mixture havingdissolved therein not more than 05 'rcent by weight of a nickel halidefrom the group consisting of nickel chloride, nickel bro- 9 10 mide andnickel iodide and not more 'than 0.1 percent 2,613,222 Specht et a1 Oct.7, 1952 by weight of a copper halide from the group consisting 2,883,418Reppe et a1 Apr. 21, 1959 of copper chloride, copper bromide and copperiodide,

releasing the pressure from the liquid withdrawn from FOREIGN PATENTSsaid reaction zone, and separating acrylic acid from the 5 872,042Germany 30, 1953 liquid.

18. A process as claimed in claim 1 in which the halide OTHER REFERENCESions are introduced at least in part by adding to such Reppe: itAcetylene Chemistry, P. B. Report, 188524;

reaction mixture a free halogen from the group consistp 161 (1949) ingof chlorine, bromine and iOdine. 10

References Cited in the file of this patent UNITED STATES PATENTS2,593,440 Hagemeyer Apr. 22, 1952

1. A PROCESS FOR THE PRODUCTION OF ACRYLIC ACID WHICH CONSISTSESSENTIALLY OF CONTACTING A GASEOUS MIXTURE OF ACETYLENE AND CARBONMONOXIDE UNDER A PRESSURE EXCEEDING 5 ATMOSPHERES AND AT TEMPERATURESBETWEEN 150* AND 250*C. WITH AN AQUEOUS REACTION MIXTURE OF WATERCONTAINING AT MOST 40% BY VOLUME OF WATER AND AT LEAST 60% BY VOLUME OFAN ORGANIC, WATER-MISCIBLE INERT SOLVENT WITH RESPECT TO THE TOTALVOLUME OF SAID WATER AND SAID SOLVENT, SAID AQUEOUS REACTION MIXTUREHAVING HOMOGENEOLY DISSOLVED THEREIN IONS OF A METAL OF THE IRON GROUP,HALIDE IONS FROM THE GROUP CONSISTING OF CHLORIDE, BROMIDE AND IODIDE,AND COPPER IONS.